Today's enterprise data centers store ever-larger amounts of business critical data that must be immediately available and highly reliable. To meet reliability requirements for critical data, arrays of groups of disks are often employed. One type of array is known as a redundant array of independent disks (RAID array). Within a RAID array, data is distributed across groups of disks (“RAID groups”) in a manner consistent with the RAID level implemented, from full mirroring to parity protection.
As applications demand larger amounts of storage, RAID arrays include many, even thousands, of disks. In order to control costs, inexpensive disk drives of the sort used in personal computers are often employed in RAID arrays. Such disks are not typically designed to work at a high duty cycle. Rather, these disks are designed to be spun down during periods of non-use. For instance, when a personal computer sits idle, the disk drive spins down and “sleeps” until a user re-engages the computer. When such disk drives are employed in RAID arrays, they often remain spun up and active indefinitely. This can cause the disk drives to fail sooner than they would if used in the environment for which they were originally designed. Furthermore, keeping all the disk drives in the RAID array spun up all the time uses relatively high power. It would be advantageous to use disk drives in RAID arrays in a manner that would extend the life of the disk drives and conserve power while offering adequate service to the customer.